Uninitialized constant Coderay (Redmine 4.1)

[peterherczeg]

Hi, after migration to latest stable Redmine (4.1.0) with a few existing Wiki pages causes Internal Server error 500 when opening.

Environment:
Redmine version 4.1.0.stable
Ruby version 2.6.3-p62 (2019-04-16) [x86_64-linux]
Rails version 5.2.4.1
coderay gem: 1.1.2

what could be the cause of this error?
thanks in advance!